A position input device has recently been used as an input device for a tablet type PC (personal computer) or the like. This position input device includes for example a position indicator formed in the shape of a pen and a position detecting device having an input surface on which pointing operations and the input of characters, figures, and the like are performed by using the position indicator.
In related art, as a pen type position indicator of this kind, a position indicator for an electromagnetic induction type position detecting device is well known. The electromagnetic induction type position indicator has a resonance circuit formed by connecting a capacitor for resonance to a coil wound around a ferrite core as an example of a magnetic core. The position indicator indicates a position on the position detecting device by transmitting and receiving a resonance signal obtained in the resonance circuit to and from a sensor of the position detecting device.
The pen type position indicator of this kind in related art is also configured to have a function of detecting a pressure (pen pressure) applied to a tip portion (pen point) of a core body and transmitting the pressure (pen pressure) to the position detecting device. In this case, for detecting the pen pressure, a method is known which uses a mechanism that changes the capacitance of the capacitor forming the resonance circuit or the inductance of the coil forming the resonance circuit according to the pen pressure.
FIGS. 12(A) and 12(B) show an example of a constitution in related art of a position indicator that includes a pen pressure detecting module of a variable capacitance capacitor type that changes the capacitance of a capacitor forming a resonance circuit of the position indicator according to pen pressure. The example is described in Patent Document 1 (Japanese Patent Laid-Open No. 2011-186803). FIG. 12(A) is a longitudinal sectional view of assistance in explaining the example of constitution of the position indicator.
As shown in FIG. 12(A), a position indicator 100 includes, within a cylindrical casing (case) 101, a core body 102, a position indicating coil 104 wound around a ferrite core 103 having a cylindrical shape, a variable capacitance capacitor 105, and a printed board 106.
The casing 101 is of a cylindrical shape having an opening portion 101a on one end side in an axial direction and closed on another end side in the axial direction. The printed board 106 having electronic parts mounted thereon is fixed close to the other end side in the axial direction within a cylindrical hollow portion of the casing 101 by fastening means such as an adhesive, a fixing screw, or the like. The ferrite core 103 is housed close to the one end side where the opening portion 101a of the casing 101 is formed.
As shown in FIG. 12(B), the ferrite core 103 is for example of a cylindrical shape having a through hole 103a in the axial direction at the position of the central axis of a circular cylinder having a perfectly round cross section. The position indicating coil 104 forming the resonance circuit is mounted in a state of being wound around the outer circumference of the ferrite core 103. Both ends, which are not shown in the figures, of the position indicating coil 104 are electrically connected to electronic parts forming the resonance circuit which electronic parts are mounted on the printed board 106. The core body 102 is inserted through the through hole 103a of the ferrite core 103.
The core body 102 is formed by a rod-shaped member having a substantially uniform thickness (diameter). The core body 102 is made of an elastic material so as not to damage an input surface formed by a glass surface or the like. One end in the axial direction of the core body 102 is a tip portion 102a having a role of a pen point. The tip portion 102a in the example of FIG. 12(A) is formed in substantially the shape of a circular cone. The tip portion 102a is projected so as to be exposed from the opening portion 101a to the outside when the core body 102 is inserted through the through hole 103a of the ferrite core 103 and housed within the casing 101. In addition, another end 102b in the axial direction of the core body 102 is coupled to the variable capacitance capacitor 105.
Though not shown in detail in FIG. 12(A), when a pressure in the axial direction is applied to the tip portion 102a of the core body 102, the variable capacitance capacitor 105 exhibits a capacitance corresponding to the pressure. That is, the variable capacitance capacitor 105 exhibits a capacitance corresponding to the pressure applied to the core body 102. Because the variable capacitance capacitor 105 forms part of the resonance circuit, the pen pressure applied to the core body 102 of the position indicator 100 can be detected on the side of the position detecting device by transmitting the resonance frequency of the resonance circuit from the position indicator 100 to the side of the position detecting device.